The production for oil and gas reserves has taken the industry to remote sites including inland and offshore locations. In addition, hydrocarbon production in remote locations has become the "norm." For example, production in deviated and multi-lateral wellbores is now very common. As a result, new and unique problems, particularly, in the completion phases have arisen. Historically, the cost for developing and maintaining hydrocarbon production has been very high in remote locations. And as production continues in these remote areas, costs have also escalated because of the unique problems encountered in producing oil and gas in difficult-to-reach locations and/or producing hydrocarbon through numerous zones. As a result production techniques in these remote areas require creative solutions to unique problems not encountered in conventional wellbores.
As one skilled in the industry may understand, hydrocarbon production rates directly affect the profitability of a wellbore. During the productive life of these wells, the well must be maintained so that hydrocarbon production and retrieval is performed in the most efficient manner and at a maximum capacity. Well operators desire maximum recovery from productive zones, and in order to maximize production, proper testing, completion and control of the well is required.
In wellbore construction, four factors are a part of every wellbore design phase: (1) the completion method most suitable for a particular well, (2) the fluid flow paths needed, (3) the completion system chosen to bring the fluids to the wellhead, and (4) the completion cost versus the production potential. The completion method chosen is an important element, and this invention relates to proper zone isolation and the most effective and efficient means to do so. More particularly, it concerns zone isolation in cased wellbores. As one in the industry might expect today, multi-lateral wellbores require cased wellbores for efficient drainage through multiple zones and/or reservoirs. In addition, many operations conventionally performed at the surface are now performed downhole. As a result, cased-hole operations have become a necessity for many wellbore completions.
Thus, different tools are needed for each of two methods of completion: (1) open-hole completion and (2) cased or perforated completions. In an open-hole or a barefoot wellbore completion, a relatively large internal diameter is encountered and the open-hole shape is invariably skewed. The open-hole is irregular (not perfectly cylindrical) since the hole is drilled in the earthen formation. Therefore, the external casing packer became an ideally suited tool to isolate zones during production or cementing operations because of its large inflation and sealing capacity. In such completion methods, the external casing packer is part of the casing string and forms a seal and an anchor against the open-hole wall when an elastomeric element in the inflatable tool is inflated. The anchor in the open-hole is formed when the packer's elastomeric element is inflated and contours to the shape of the open-hole, preventing axial movement in the wellbore. The exceptional expansion and sealing capabilities of the flexible elastomeric elements allow these tools to handle conditions that would be impossible for conventional packing tools. When inflated, the packing element conforms to virtually any irregularity in open-hole completed wellbores. While no packing element can tolerate all conditions, the inflatable packing elements have been found to be very tolerant for open-hole completions.
On the other hand, in cased-hole wellbores, a different set of criteria and problems for completing and workover of a wellbore are encountered. One recent problem that has been encountered is to isolate a particular zone that is located below completion equipment already located in the wellbore. Such zones are normally very difficult to isolate since only limited access or through-pass in existing wellbore equipment is available to the zone below. Conventionally, such completion equipment has provided a relatively narrow access to a section located below. In such wellbores there is, therefore, a need for zone isolation packers that may be installed below any existing equipment. It is clear that conventional packer equipment may not be used in such wellbores since much of it comprises larger diameter equipment. Such equipment, therefore, cannot pass through the restricted available access.
In addition, conventional thru-tubing and production injection packer technologies are also inadequate in these applications since they do not and cannot provide sufficient sealing capability in larger diameter casing sizes when using an inflation medium that operates under a phase change condition. Examples of a phase change medium include cement or epoxy. Phase change of an inflation medium occurs after the inflation medium sets. An inflation medium sets when it retains a permanent phase. For example, a phase change occurs when cement or epoxy hardens. However, subsequent to such hardening, another phase change occurs such that the cement or epoxy shrinks slightly.
In these restricted access wellbores, conventional production injection packers and thru-tubing technology using phase change inflation media cannot be inflated to reach the outer diameter (OD) of the cased wellbore (the wall) to effectively seal a zone for reasons that will be discussed hereinafter. Thus, a new zone isolation tool is greatly needed to isolate certain zones in the cased wellbore.
One concept is to use conventional external casing packer technology, now used in larger diameter open-hole completions, to anchor and seal (isolate) a particular zone, especially since they have a relatively small "pass-through" OD and thus are capable of passing through the restricted access of existing equipment. Examples of these conventional packer technology include "production injection packers" and "thru-tubing packers." However, even with improving elastomer technology, these conventional packers have proven to be relatively ineffective in applications requiring inflation in a cased wellbore with a phase change medium.
In order to understand why this is so, it is first necessary to review the design of these (inflatable) packers. Inflatable packers have long utilized a design incorporating the use of various elastomeric elements in combination with metal slats or ribs as inflatable elements. Such inflatable tools comprise an elastomeric sleeve element mounted in surrounding relationship to a tubular body portion. To protect the elastomeric sleeve element, a plurality of resilient slats or ribs are peripherally bonded to the elastomeric sleeve element. The medial portion of the elastomeric sleeve is further surrounded, and may be bonded, by an outer annular elastomeric sleeve element or "cover" of substantial thickness. These prior art external casing packers thus use a "full cover" design. Upper and lower assemblies securely and sealingly couple the ends of the packing element sleeves to the central tubular body. A pressurized phase change inflation medium is communicated to the tubular body and then through radial passages thereon to the interior of the elastomeric sleeve element to inflate the packing elements, providing a sealing radial engagement with the wellbore wall.
A conventional external casing packer (with or without a phase change medium) is ineffective in cased-wellbore applications because the contour of the casing is sufficiently cylindrical, thus preventing a proper anchoring relationship between the external casing packer and the casing wall. One reason a proper anchor does not result is because the coefficient of friction between the elastomeric element and the steel casing in a wetted media environment is very low. Thus, the differential pressure in the wellbore between locations above and below the packer forces its movement.
In addition, the conventional external casing packer is designed to provide only anti-extrusion benefits. For example, the ribs are located only on the secured ends (securing assemblies) of the elastomeric element and thus provide only limited anchoring benefits. As such, the elastomeric element has a tendency to "roll over" or overlap the secured end when a sufficient axial force is applied to the ribs. On the other hand, if a modification is made and the elastomeric element is fully ribbed, another disadvantage arises. In the latter case, a full length rib elastomeric element, in combination with the elastomeric element, is a much larger OD packer. Therefore, a new design requires a thinner cover to overcome the limited access available through existing downhole equipment.
However, when a thinner cover is introduced in the new design, another significant problem arises when a phase change inflation medium is used to inflate the inflatable packer in the cased wellbore. This new problem arises when the inflation medium changes phases (cures and contracts) and there is a resulting loss of radial force available against the casing wall. It is understood by one skilled in the art that a relatively thicker elastomeric element normally makes up this differential in radial force. However, when a thinner element is used, the loss in radial force may not be compensated or "made up." Thus, the amount of compensation an elastomeric element can "make-up" is a function of its thickness. Stated differently, the energy storage capacity of the elastomeric element available for sealing engagement is a function of its thickness. Thus, as a relatively thicker elastomeric element is used, a relatively larger energy storage potential exists. This larger stored energy potential is available to act against the cased-wellbore wall in sealing engagement, compensating for any shrinkage in the inflation medium. In a cased wellbore, therefore, a relatively thick elastomeric element is required to obtain proper sealing capability. Thus, there is a need for a new zone isolation tool that overcomes all of these limitations.
Various prior art external casing packer devices have existed, but none provide a solution for isolating a zone below existing equipment that has restricted access in a cased wellbore environment. For example, Mody, et. al., discloses in U.S. Pat. No. 5,143,154 an inflatable packing element for an inflatable packer having a specific rib coupling design to the tubular mandrel.
Another teaching is that by Mody in U.S. Pat. No. 5,101,908 for an inflatable packing device and a method for sealing. The device discloses upper and lower elastomeric elements surrounding a tubular mandrel. Again, however, this teaching is not directed to the problems encountered herein.
Another teaching is that of Halbardier in U.S. Pat. No. 4,869,325, disclosing a method and apparatus for setting, unsetting, and retrieving a packer or a bridge plug from a subterranean well which may be passed though a small diameter tubing. However, again, such a teaching is not directed to the specific problems encountered herein.
Therefore, there is a need for a method and apparatus for an inflatable tool that provides a solution for isolating zones through restricted access completion equipment in a cased wellbores that provide both a seal and anchoring features.